Analog vs Digital signals

Analog Signal:-
An analog signal is a continuous wave denoted by a sine wave (pictured below) and may vary in signal strength (amplitude) or frequency (time). The sine wave's amplitude value can be seen as the higher and lower points of the wave, while the frequency (time) value is measured in the sine wave's physical length from left to right.

There are many examples of analog signals around us. The sound from a human voice is analog, because sound waves are continuous, as is our own vision, because we see various shapes and colors in a continuous manner due to light waves. Even a typical kitchen clock having its hands moving continuously can be represented as an analog signal.
                                                           

Digital Signal:-
A digital signal - a must for computer processing - is described as using binary (0s and 1s), and therefore, cannot take on any fractional values. As illustrated in the graphic below, digital signals retain a uniform structure, providing a constant and consistent signal. Because of the inherent reliability of the digital signal, technology using it is rapidly replacing a large percentage of analog applications and devices. For example, the wristwatch, showing the time of day, with its minute, hour, and sweeping second hands, is being replaced by the digital watch, which offers the time of day and other information using a numerical display. A typical digital signal is represented by 1s and 0s .
                                                         

        

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GUIDED MEDIA or WIRED MEDIA

GUIDED MEDIA or WIRED MEDIA :-
-Electrical/Optical signals are passed through a solid medium (different types of cables/wires)
-As the path traversed by the signals is guided by the size, shape and length of the wire, this type of media is called guided media.
-Also, in guided media, the signals are confined within the wire and do not propogate outside of the wire/media.
-E.g., Copper Unshielded Twisted Pair (UTP), Copper Shielded Twisted Pair (STP), Copper Co-axial cables, Fiber Optic Cables.


Twisted Pair Copper:
-It is the most widely deployed media type across the world, as the last mile telephone link connecting  every home with the local telephone exchange is made of twisted pair copper. These telephone lines are reused as last mile DSL access links to access the internet from home.
-They are also used in Ethernet LAN cables within homes and offices.
They support  low to High Data Rates (in order of Giga bits)
However, they are effective only upto a maximum distance of a few kilometres/miles, as the signal strength is lost significantly beyond this distance.
-They come in two variants, namely UTP (unshielded twisted pair) and STP (shielded twisted pair). Within each variant, there are multiple sub-variants, based on the thickness of the material (like UTP-3, UTP-5, UTP-7 etc.)
-E.g. DSL, 10/100/1000Mbps Ethernet cables


Copper Co-axial Cables
-Co-axial copper cables have an inner copper conductor and an outer copper shield, separated by a di-electric insulating material, to prevent signal losses.
-It is primarily used in cable TV networks and as trunk lines between telecommunication equipments.
-It serves as an internet access line from the home.
 -It supports medium to High Data Rates
 -It has much better immunity to noise and hence signal strength is retained for longer distances than in copper twisted pair media.


Fiber Optic Cables
-Here, information is transmitted by propogation of optical signals (light) through fiber optic cables and not through electrical/electromagnetic signals. Due to this, fiber optics communication supports longer distances as there is no electrical interference.
-As the name indicates, fiber optic cables are made of very thin strands of glass (silica).
-As they support very high data rates, fiber optic lines are used as WAN backbone and trunk lines between data exchange equipments.
-They are also used for accessing internet from home through FTTH (Fiber-To-The-Home) lines.
-Additionally, they are used even for LAN environment with different LAN technologies like Fast Ethernet, Gigabit Ethernet etc. using optical links at the physical layer.
 - OC-48, OC-192, FTTC, HFC are examples of Fiber Optical links.


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what is transmission medium || Types of transmission media

Transmission Medium:-
Data is represented by computers and other telecommunication devices using signals. Signals are transmitted in the form of electromagnetic energy from one device to another. Electromagnetic signals travel through vacuum, air or other transmission mediums to move from one point to another(from sender to receiver).

Electromagnetic energy (includes electrical and magnetic fields) consists of power, voice, visible light, radio waves, ultraviolet light, gamma rays etc.

Transmission medium is the means through which we send our data from one place to another. The first layer (physical layer) of Communication Networks OSI Seven layer model is dedicated to the transmission media.
Types of Transmission media:-
1. Guided media (wired media)
2. Unguided media (wireless media)

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The TCP/IP Reference Model

The TCP/IP Reference Model
TCP/IP means Transmission Control Protocol and Internet Protocol. It is the network model used in the current Internet architecture as well. Protocols are set of rules which govern every possible communication over a network. These protocols describe the movement of data between the source and destination or the internet.

1. host to network layer
    -Lowest layer of the all.
    -Protocol is used to connect to the host, so that the packets can
      be sent over it.
    -Varies from host to host and network to network.

2. Internet layer
   -Selection of a packet switching network which is based on a
    connectionless internetwork layer is called a internet layer.
   -It is the layer which holds the whole architecture together.
   -It helps the packet to travel independently to the destination.
   -Order in which packets are received is different from the way
    they are sent.
   -IP (Internet Protocol) is used in this layer.

3. Transport layer
    -It decides if data transmission should be on parallel path or
     single path.
   -Functions such as multiplexing, segmenting or splitting on the
    data is done by transport layer.
   -The applications can read and write to the transport layer.
   -Transport layer adds header information to the data.
   -Transport layer breaks the message (data) into small units so
     that they are handled more efficiently by the network layer.
   -Transport layer also arrange the packets to be sent, in sequence.

4. Application layer
 The TCP/IP specifications described a lot of applications that   were at the top of the protocol stack. Some of them were TELNET, FTP, SMTP, DNS etc.

 -TELNET is a two-way communication protocol which allows
  connecting to a remote machine and run applications on it.
 -FTP(File Transfer Protocol) is a protocol, that allows File transfer
  amongst computer users connected over a network. It is reliable,
  simple and efficient.
 -SMTP(Simple Mail Transport Protocol) is a protocol, which is
  used to transport electronic mail between a source and
  destination, directed via a route.
 -DNS(Domain Name Server) resolves an IP address into a textual
  address for Hosts connected over a network.
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OSI Reference Model

OSI (Open Systems Interconnection) is reference model for how applications can communicate over a network. A reference model is a conceptual framework for understanding relationships.

OSI Layers:-
Layer 7 - Application
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical

OSI Model, Layer 7, supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.
Layer 7 Application examples include WWW browsers, NFS, SNMP, Telnet, HTTP, FTP.

Presentation (Layer 6)
This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.
Layer 6 Presentation examples include encryption, ASCII, EBCDIC, TIFF, GIF, PICT, JPEG, MPEG, MIDI.

Session (Layer 5)
This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.
Layer 5 Session examples include NFS, NetBios names, RPC, SQL.

Transport (Layer 4)
OSI Model, Layer 4, provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.
Layer 4 Transport examples include SPX, TCP, UDP.

Network (Layer 3)
Layer 3 provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.
Layer 3 Network examples include AppleTalk DDP, IP, IPX.

Data Link (Layer 2)
At OSI Model, Layer 2, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.
Layer 2 Data Link examples include PPP, FDDI, ATM, IEEE 802.5/ 802.2, IEEE 802.3/802.2, HDLC, Frame Relay.

Physical (Layer 1)
OSI Model, Layer 1 conveys the bit stream - electrical impulse, light or radio signal — through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.
Layer 1 Physical examples include Ethernet, FDDI, B8ZS, V.35, V.24, RJ45.

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reference models || network architectures

Reference Models in Communication Networks
The most important reference models are :

1. OSI reference model:- has 7 layers
       
         7. Application layer
         6. Presentation layer
         5. Session layer
         4. Transport layer
         3. Network layer
         2. Data link layer
         1. Physical layer

2. TCP/IP reference model:-
       
         4. Application layer
         3. Transport layer
         2. Network layer / Internet layer
         1. Physical layer / Host-to-network layer

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Network Topology

network topology describes the layout or appearance of a network that is, how the computers, cables and other components within a data communication network are interconnected , both physically and logically.

TYPES:
1. Bus topology
2. Ring topology
3. Star topology
4. Tree topology
5. Mesh topology
6. Hybrid topology

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